Their geographic isolation may have been caused by the desertification of a region in west Africa called the Dahomey Gap that separated the forests in central Africa from the forests in west Africa. Other potential barriers between the two regions include the Niger River Delta and the volcanic region of southwestern Cameroon. Based on their genetic data, the UCSD biologists believe that the west African populations have been isolated for as long as 2.4 million years.
The UCSD scientists note in their paper that while their genetic analyses of the mitochondrial, or maternally inherited, DNA sequences and nuclear microsatellite loci (short repetitive segments of DNA that show differences among populations and individuals) suggest the existence of "three recognizable taxa of African elephants," their results need to be confirmed before a formal taxonomic revision of the African elephants is proposed. That confirmation would require examination of additional nuclear DNA sequences which are inherited paternally as well as maternally.
"If the level of genetic differentiation between the three taxa identified here is confirmed to reflect several million years of divergence, it will be appropriate to treat them as species in recognition of their long independent evolutionary trajectories," they write in their paper.
Because nearly all of the African elephants in zoos are savanna elephants, the results do not have implications for elephants now in captivity. Zoos do not have forest elephants, largely because they are so elusive, and only three western elephants are now in captivity at the Abidjan Zoo in Cte d'Ivoire. However, the results have widespread implications for the management of all three types of wild African elephants. Although the ivory trade ban has slowed the slaughter of elephants, some countries have appealed for permission to resume the harvest.